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• Microwave is best treatment on transglutaminase (TGase)-induced whey protein isolate. • Ultrasound-microwave promoted the reaction of whey protein isolate and TGase. • Ultrasound-microwave enhanced properties of TGase-induced whey protein isolate. In the present study, ultrasound (400 W, U), microwave heating (75 ℃ for 15 min, M) and ultrasound synergized with microwave heating (UM) pretreatments of whey protein isolate (WPI) were applied to investigate and compare their influence on structure, physicochemical and functional characteristic of transglutaminase (TGase)-induced WPI. From the results of size exclusion chromatography, it could be seen that all three physical pretreatments could promote the formation of polymers in TGase cross-linked WPI, whose polymer amounts were increased by the order of U, UM and M pretreatment. Among three physical methods, M pretreatment had the strongest effect on structure and functional characteristics of TGase-induced WPI. Furthermore, compared with TGase-induced WPI, α-helix and β-turn of M−treated TGase-induced WPI (M−WPI−TGase) were reduced by 7.86% and 2.93%, whereas its β-sheet and irregular curl were increased by 15.37% and 7.23%. Zeta potential, emulsion stability and foaming stability of M−WPI−TGase were increased by 7.8%, 59.27% and 28.95%, respectively. This experiment exhibited that M was a more effective pretreatment method than U, UM for WPI, which could promote its reaction with TGase and improve its functional properties. [ABSTRACT FROM AUTHOR]

The effects of different concentrations of safflower yellow (SY) on the structure and emulsifying properties of whey protein isolate (WPI)-SY complexes were investigated at 25 °C for 0, 3 and 6 days. About 92.6%, 93.75%, and 95.47% of the free sulfhydryl groups from the WPI-SY complexes were lost over 0, 3 and 6 days, respectively, in the presence of 2% SY. Meanwhile, the fluorescence intensity of the WPI-SY complexes also weakened obviously, indicating that the tryptophan residues micro-environment underwent certain changes. Furthermore, fourier transform infrared spectroscopy demonstrated that SY increased the proportion of WPI β-sheets and decreased the proportion of β-turn structures. The particle size of the WPI-SY complexes increased as the SY concentration was increased from 1 to 4%. Compared with SY or WPI, the antioxidant activity of the WPI-SY complexes was enhanced with SY ranged from 0.25 to 4%. SY triggered emulsifying activity of WPI initially increased and then decreased. Therefore, SY could enhance the emulsifying properties and antioxidant activities of WPI-SY. • β-Structures in whey protein isolate (WPI) had been changed after binding SY. • SY might induce WPI to generate macro-molecular polymer. • WPI-SY complexes had better antioxidant activities and emulsifying properties. [ABSTRACT FROM AUTHOR]

Impacts of ultrafiltration and hydrolysis on antioxidant abilities of Maillard reaction products (MRPs) derived from whey protein isolate (WPI) and galactose (Gal), were evaluated in this study. Fraction (MW > 50 kDa)of WPI-Gal MRPs prepared with ultrafiltration, had the strongest antioxidant activity. The trichloroacetic acid (TCA, 2–8%) treatment could effectively enhanced antioxidant activities of WPI-Gal MRPs. WPI-Gal MRPs had higher degrees of hydrolysis and antioxidant activity than heated WPI. With hydrolysis time of pepsin and trypsin extended up, degrees of hydrolysis and antioxidant activities of WPI-Gal MRPs and WPI gradually increased (P < 0.05). Furthermore, reverse phase HPLC analysis showed that WPI-Gal MRPs was easier to be hydrolyzed and had smaller molecular peptides than heated WPI. • Fractions (MW > 50 kDa) of WPI-Gal MRPs had the strongest antioxidant activity. • TCA treatment effectively enhanced antioxidant activities of WPI-Gal MRPs. • WPI-Gal MRPs had higher hydrolysis degrees and antioxidant activity than heated WPI. [ABSTRACT FROM AUTHOR]